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Plasma Osmolality Calculator

Calculate plasma osmolality to screen for hyperosmolar states or dehydration.

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Input Parameters

Enter details for calculation.

Plasma Osmolality

290.4 mOsm/kg
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Expert Tip

Normal range is 275-295 mOsm/kg. Elevated values indicate dehydration, diabetic ketoacidosis, or toxic ingestions.

Calculation Methodology & Details

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Formula

Calculated Osmolality = 2×Na + Glucose/18 + BUN/2.8

Estimates the major solute concentrations contributing to blood osmolality.

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Important Disclaimer

The calculations provided are for educational and general informational purposes only. They do not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.

How Osmolality is Calculated

Follow these steps to use this calculator:

1

Enter Labs

Sodium, BUN, and glucose levels.

2

Read Osmolality

Compare to clinical reference levels.

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FLUIDS

Osmolal Gap

Osmolal gap.

Launch Tool

Detailed Insights & Expert Guide

ℹ️ About this Calculation

This clinical electrolyte and fluid resuscitation calculator assists healthcare professionals with osmolality assessment, electrolyte deficit calculations, IV infusion rate adjustments, and fluid management protocols based on intensive care guidelines.

Variable Glossary

Input

Serum & Fluid Metrics

Serum sodium, potassium, calcium, glucose, BUN, albumin, patient body weight, or IV volume parameters.

Parameter

Resuscitation Targets

Corrected serum sodium/calcium, free water deficit (L), hourly IV drip rate (mL/hr), and calculated osmolality (mOsm/kg).

How to Calculate Step-by-Step

1

Step 1

Enter current serum electrolyte levels, blood chemistry lab results, or total IV volume ordered.

2

Step 2

Input patient weight and clinical correction factors (such as hyperglycemic sodium adjustment or albumin level).

3

Step 3

Review calculated deficit totals, corrected electrolyte values, and recommended IV infusion rates.

FAQ

Why is sodium correction necessary in hyperglycemia?
Elevated blood glucose shifts water from intracellular to extracellular spaces, artificially diluting serum sodium. Corrected sodium accounts for this osmotic shift (adding ~1.6 to 2.0 mEq/L per 100 mg/dL glucose over 100 mg/dL).
How is maintenance fluid calculated using the Holliday-Segar method?
The 4-2-1 rule allocates 4 mL/kg/hr for the first 10 kg of body weight, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr for each remaining kg.
Can fluid deficit calculators replace clinical re-evaluation?
No. Electrolyte replacement and fluid correction require continuous clinical monitoring, serial blood labs, and careful rate control to prevent complications like central pontine myelinolysis or cerebral edema.